We propose to continue our investigations into the manner by which hallucinogenic drugs produce changes in sensory, associative and motor processes. The main procedures to be used will involve the classical (Pavlovian) conditioning paradigm whose essential feature is a set of experimental operations involving an aversive or apppetitive unconditioned stimulus (UCS), which reliably produces a measurable unconditioned response (UCR), and a conditioned stimulus (CS) that has been shown by empirical test not to initially produce a response resembling the UCR. The CS and UCS are then presented repeatedly to the organism in a specified order and temporal spacing, and a response similar to the UCR develops to the CS that is called the conditioned response (CR). The analytical power of this paradigm is the ability to exactly specify the stimulus conditions governing acquisition, as well as other aspects of learned behavior and to delineate the associative effects of the variables of interest from their effects on nonassociative processes. Accordingly, we are interested in comparing the effects of LSD and other hallucinogens (Psilocin, DMT, DOM and mescaline) on acquisition in classical defense (rabbit nictitating membrane) and classical reward (rabbit jaw movement) conditioning in order to determine a common effect of hallucinogens on such acquisition processes that is not shared by inactive compounds such as BOL, bufotenine or amphetamine. Drug effects on associative processes will be further analyzed to determine whether they are due to effects on sensory processing of the CS and UCS as, for example, by a change in CS and UCS excitability functions, and/or to an effect on the final common pathway of the motor response, i.e., the abducens (VIth cranial) nucleus. Similar studies will be carried out to determine the effects of hallucinogens on conditioned inhibitory processes. Finally, we will examine the anatomical locus of drug action and attempt to determine the neurochemical systems through which they exert their effects.